The present invention refers to electro-analytical measuring equipment for the selective, rapid and high-precision determination of the concentration and the ion-activity of stationary or flowing solutions or of the partial pressure of gases.
It is well known that the size of a measuring signal, e.g. membrane potential, arising on an electro-analytical sensing element of traditional construction, e.g. anion-selective membrane, is determined not only by the electrochemical parameter, e.g. ion-concentration, of the sample to be analyzed, but it is also affected by the quality, the geometrical construction and the extent of the incidental impurity of the material of the sensing element; even more, by its life, reckoned from the date of production, etc. as well. Consequently, the measuring signal arising in the course of measurement appears as the resultant of all the above listed facts. Thus, it is clear from the above that the change of the measuring signal resulting from the change of the electrochemical parameter to be measured, e.g. from the increase or the decrease of the ion-concentration, cannot be distinguished from the effect of the change of a disturbing character in the material or the condition of the sensing element.
Obviously, traditional measuring technique, calibration, standard addition, setting of the constant ion-intensity, programming of slope, etc., see e.g. Havas: Ion and molecule selective electrodes in biological systems. Latest results of chemistry, published by: Akademiai Kiado in 1980, pages 80 to 87, does not strive, since it cannot strive to determine the extent of the fault-signal resulting from the disturbances already mentioned. All things considered, the methods known till now may be attributed to the comparison of the relevant electrochemical parameters of the sample and of one or more liquids, standard-solution or gas, of a known composition. It means that before the measurement is carried out, the electronic behavior of the measuring equipment and the electrochemical behavior of the measuring cell are to be harmonized (this is called: matching).
As a consequence of the uncontrollable irregularity of the disturbances occurring, the accuracy of the measurements depends obviously on the frequency of the above matching or matchings. In precision measurements it is required to carry out some matching prior to each and every measurement (at least for the sake of control). If the time necessary for the indispensable flushing of the measuring cell is also considered, the total period of the analysis will be (in the case where two standard liquids are applied) approximately five times more than the actual period of the measurements. Though by "one-spot" matching wide spread in electro-analytics this period may be reduced to one half, there is a fault resulting from the interim change of the response-function slope of the measuring cell that cannot be eliminated.
It is obvious from the above that the total period of the precision analyses is considerably long (because of the matching steps between factual measurements). On the other hand, it is impossible to carry out continuous, and at the same time high-precision measurements, as the construction of traditional measuring cells does not facilitate the determination of the fault signals during measurement, not speaking of matching to be performed simultaneously with the measurement.